Extremely rare corrosion within a motor component ultimately caused an otherwise mechanically sound helicopter to fall into the icy sea earlier this year, killing two pilots aboard, the military said Sunday as it wrapped up its investigation of the mysterious crash.
The AS565 Panther helicopter — known in the IAF as an “Atalef,” or bat — slammed into the water just off the coast of the northern city of Haifa on January 3. The two pilots, Lt. Col. Erez Sachyani and Maj. Chen Fogel, were killed but a third officer on board, Cpt. Ron Birman, managed to jump out and was rescued with relatively minor injuries.
The final report largely confirmed interim findings published by the army just one month after the crash.
According to the investigation, the malfunction was a result of corrosion that maintenance failed to identify, as the component in question is located well within the motor and is therefore not part of the routine checks recommended by the manufacturer, France-based Airbus Helicopters.
The military said the first-of-its-kind malfunction was not known to either manufacturer or the Air Force.
In its final report, the IDF said the corrosion was likely caused due to the aircraft’s constant proximity to the sea. The “Atalef” fleet is capable of landing on Israeli Navy missile ships and is primarily used for missions at sea.
The report added that the engine “rinsing process,” which aims to prevent corrosion, was “not optimal,” and was not carried out “exactly” according to the manufacturer’s instructions.
According to the report, the helicopter was due to undergo a more comprehensive inspection by the manufacturer after another 250 flight hours. It last had a full inspection, which is supposed to be scheduled every 1,650 flight hours, in 2017.
Instead, the corroded piece caused the turbine blade to break off, sparking a fire in the left motor that quickly spread to the right, filling the cabin with smoke. The military blamed engine components that were not fireproof at the “required temperature,” such as aluminum, for allowing the fire to spread.
“This is due to a problem with the manufacturer’s design. Following this, the helicopter manufacturer will release safety information regarding the aluminum components in the engine,” the IDF said.
There was no immediate comment from Airbus Helicopter or its parent company Airbus.
Sachyani and Fogel maintained control of the aircraft and tried to put out the fire with an onboard extinguisher system while bringing it down for a water landing using a flotation system built into the helicopter.
The probe determined that the force of the impact with the water either knocked Sachyani and Fogel unconscious entirely or at least disoriented them enough that they were unable to unbuckle their seat belts or use the oxygen tanks in the cabin as the helicopter began to sink.
The two are believed to have drowned shortly after impact. Rescuers, who arrived within eight minutes of the crash, would not have been able to pull them out alive, the investigation found.
The final findings of the probe were presented to Sachyani’s and Fogel’s families, the military said.
The investigation determined that the pilots were calm and in control during the malfunction and handled themselves relatively well. But it also found that the pilots did not turn off the motors before turning on the fire suppression system, which prevented it from performing at full capacity.
“We emphasize that the crew was competent, skilled, and faced a sequence of challenging malfunctions… in complex flight conditions in the dark of night over the sea,” the military said on Sunday.
After the crash, former IAF chief Amikam Norkin grounded the air force’s fleet of AS565 Panther helicopters. They remained out of service due to initial difficulties in determining the cause of the malfunction. With the discovery that a corroded blade was responsible, the air force sent off all the remaining helicopters for a check to ensure that they do not have a similar problem, and has began to return them gradually to normal service.
“An in-depth, professional, and thorough investigation was conducted here,” IDF chief Aviv Kohavi said. “We lost two of our best pilots in this accident. Our task now is to study the conclusions and lessons learned, and prevent the next accident.”
Judah Ari Gross contributed to this report.